In the mass production of expanded, extruded, starch-based foods such as ready-to-eat (RTE) cereals and snacks, extrusion cooking may be employed to achieve high production rates and desirable product attributes such as low bulk densities, uniform cell structure, crisp or crunchy textures, and in the case of RTE cereals, long bowl life. Fortification of extruded, expanded foods such as ready-to-eat (RTE) cereals and snacks with insoluble and soluble dietary fiber as a replacement for higher calorie starch-based components such as wheat flour may adversely affect extrusion functionality or extrudability of the formulation. For example, production rates may decrease, extruder surging may increase, or product attributes such as bulk density, cell structure, texture, taste, mouth-feel, and bowl life may suffer as a result of substituting dietary fiber for starch-based components such as wheat flour. Generally, dietary fiber has a substantially higher water holding capacity than starch-based components such as wheat flour. The dietary fiber absorbs large amounts of water which makes it more difficult to expand a snack or RTE formulation and to achieve low bulk densities, uniform cell structure, and crispiness comparable to a starch-based formulation which does not contain fortifying amounts of dietary fiber. Decreasing the amount of added water to achieve a lower bulk density increases dough viscosity which tends to result in higher extruder back pressures, and reduced throughput or production rates. Production rate problems and product attribute problems tend to increase as greater amounts of dietary fiber are used to replace the starch-based components such as wheat flour.
Dietary fiber fortification of expanded snacks and RTE cereals has generally been achieved with bran, or the outer, generally non-digestible outer coating of whole grains, such as wheat bran and corn bran as disclosed in U.S. Pat. Nos. 4,777,045 to Vanderveer et al, U.S. Pat. Nos. 4,756,921 and 4,837,112 each to Calandro et al, 5,169,662 to Spicer, and U.S. Pat. No. 5,176,936 to Creighton et al. However, according to U.S. Pat. No. 5,480,669, the addition of resistant starch to dough compositions that are intended to be cooker extruded will yield a fiber fortified food product that has increased expansion over food products that do not contain the resistant starch or that are fortified with other forms of dietary fiber, such as oat bran or wheat bran.
Enzyme-resistant starch (RS) is a fraction of starch not digested in the small intestine of healthy individuals. Certain types of resistant starch may be partially fermented by microflora in the large bowel. Resistant starch may be classified into four types. Physically inaccessible starch, which is locked in the plant cell, is classified as type I resistant starch. It can be found in foodstuffs with partially milled grains and seeds and legumes. Native granular starch found in uncooked ready-to-eat starch-containing foods, such as in bananas, is classified as type II resistant starch. Enzyme susceptibility of type II resistant starch is reduced by the high density and the partial crystallinity of the granular starch. Type I and type II resistant starches have low melting points and do not survive high temperature processing, such as extrusion.
Starch may be treated to obtain an indigestible starch fraction. Depending upon the type of treatment, a type III or a type IV resistant starch may be produced. In type IV resistant starch, the enzyme resistance is introduced by chemically or thermally modifying the starch. The modification may be the formation of glycosidic bonds, other than alpha-(1-4) or alpha-(1-6) bonds, by heat treatments. Formation of these other glycosidic bonds may reduce the availability of starch for amylolitic enzymes. In addition, the digestibility of starch may be reduced by cross-linking or the presence of various substituents such as hydroxypropyl groups. However, legal limitations by the U.S. Food and Drug Administration (FDA) have been placed upon the use of various chemically modified starches in foods.
An indigestible starch fraction that forms after certain heat-moisture treatments of the starch is a type III enzyme-resistant starch. Heat-moisture treatments of the starch create crystalline regions, without the formation of glycosidic bonds other than alpha-(1-4) or alpha-(1-6) bonds. The type III resistant starch is thermally very stable, which is highly advantageous for producing reduced-calorie extruded cereals provided it is not substantially adversely affected by medium to high shear conditions encountered during extrusion. If the crystal structure that provides enzyme resistance is destroyed or melts during extrusion, and if the crystal recrystallizes into a lower-melting form that is not enzyme resistant, then calorie reduction will not be achieved in the extruded product.
U.S. Pat. Nos. 6,013,299, 6,352,733, and 6,613,373, U.S. Patent Publication No. 2004/0047963, and International Patent Publication No. WO 99/22606, published May 14, 1999, each to Haynes et al. disclose a method for producing a starch-based composition comprising a type III, retrograded, enzyme-resistant starch which has a melting point of at least about 140° C. Haynes et al also disclose a flour substitute comprising substantially ungelatinized wheat flour and a gelatinized, starch-based bulking agent, which comprises at least about 25% by weight of an amylase-resistant starch type III, based upon the total starch content of the starch-based bulking agent. The resistant starch ingredient has a melting enthalpy of from about 0.5 Joules/g to about 4.0 Joules/g at a temperature of from about 130° C. to about 160° C. as determined by modulated differential scanning calorimetry (MDSC), and a water-holding capacity of less than 3 grams of water per gram of dry resistant starch ingredient. The resistant starch has a melting point or endothermic peak temperature of at least about 140° C. as determined by MDSC. The enzyme resistant starch type III, it is disclosed, may be used to produce a baked good such as a cracker, cookie or reduced calorie cookie where the resistant starch ingredient is substantially unaltered by baking. The food product of Haynes et al may be a bar-type product, extruded, sheeted and cut, or rotary molded.
The present invention provides a process for the mass production of extruded, directly expanded food products such as ready-to-eat (RTE) cereals and expanded snacks having a high dietary fiber content. The fortification of extruded, expanded foods such as ready-to-eat (RTE) cereals and snacks with dietary fiber as a replacement for higher calorie starch-based components such as wheat flour may be achieved with both high production rates and desirable product attributes comparable to those of the non-fiber fortified product. It has been found that use of a starch-based composition comprising an enzyme-resistant starch type III which has a melting point of at least about 140° C., as determined by differential scanning calorimetry (DSC), and a water holding capacity of less than 3 grams of water per gram of dry resistant starch ingredient provides unexpectedly superior extrusion functionality and extrudability compared to the use of other resistant starches in the production of extruded, directly expanded food products. The extruded, expanded food products, such as RTE cereals produced in accordance with the present invention exhibit excellent extrusion characteristics in terms of bulk density, moisture content, a crispy, crunchy texture, bowl life, and cell structure. The expanded products may be produced at unexpectedly high production rates using large amounts of resistant starch for large caloric reductions when compared to rates and caloric reductions using other resistant starches such as a type II or type IV resistant starches, or lower melting type III resistant starches, which tend to be destroyed under high temperature and high shear processing, such as extrusion.